This invention relates to an adjustable stub guard assembly for the sickle knife of a crop cutting apparatus such as a swather or combine harvester.
The cutting knife of a crop cutting apparatus of this type generally comprises a horizontal support bar or flange supported on the apparatus for movement across the ground in a cutting action. On the support bar is mounted a plurality of stub guards which are arranged in pairs with one clamped above the support bar and the other clamped below the support bar at a position aligned with the upper stub guard. Generally each stub guard is formed as an integral cast body defining a pair of forwardly projecting fingers which are connected by transverse bars with the fingers of the upper stub guard cooperating with the fingers of the lower stub guard to define a channel across the front of the support bar within which a reciprocating knife is guided.
To obtain a proper cutting action it is necessary to adjust the spacing between the upper stub guard and the lower stub guard to accurately confine the knife and cause a cutting action between the knife blades and machined surfaces on the stub guards. The adjustment must be controlled within narrow tolerances to optimize the cutting action without providing excessive frictional engagement between the stub guards and the knife in its reciprocating movement.
Conventionally this adjustment is provided by shims which are inserted between the stub guards and the support bar. However this technique is an inaccurate, inconvenient and time consuming process which must be regularly repeated during routine maintenance of the equipment in view of wear which occurs between the knife arrangement and the stub guards.
One proposal has been put forward by Hesston Corporation and is described in French patent application No: 2,546,367 in which the upper stub guard is modified so that it includes an adjustment plate which is clamped between the support bar and the under surface of the upper stub guard. The height of the adjustment plate from the support bar is then adjusted by the insertion of shims on the clamping bolts clamping the upper and lower stub guards together. The upper stub guard is in addition modified by the insertion of set screws which engage upon the upper surface of the adjustment plate so as to adjust the angle between the upper stub guard and the adjustment plate and thus vary the dimensions of the channel through which the knife arrangement runs.
This proposal is however unsatisfactory for a number of reasons and it is one object of the present invention to provide a further improved crop cutting apparatus of this general type in which adjustment of the stub guards can be obtained while using a device of simple and economic construction.